Evaluation of surface-bonded polyethylene glycol and polyethylene imine in capillary electrophoresis

A procedure for bonding polyethylene glycol (PEG) and polyethylene imine (PEI) onto the capillary surface through a highly crosslinked polysiloxane layer containing epoxy groups has been developed. Systematic variation of the coatings can be used to (a) allow separations over a pH range of 3 to 9, (b) provide for adjustment of electro-osmotic flow, and (c) reduce the adsorption of peptides and proteins. The variation of electroosmotic flow on these coated columns at different operational conditions can be explained using electrical double layer theory. Separations of substituted aromatic compounds and peptides on these coated columns were much improved over similar separations on untreated columns. The results indicate that PEI coated columns are suitable for the separation of basic proteins and PEG coated columns are suitable for acidic proteins. Separations of simple oligonucleotides which differ by only one base were also achieved.